Not applicable
The present invention pertains to oxy-fuel methods and devices for producing elevated temperatures in industrial melting furnaces for such diverse products as metals, glass, ceramic materials and the like. In particular, the present invention pertains to combustion and methods and apparatus for continuation of combustion in the event of curtailed or terminated availability of oxygen for the oxy-fuel process.
Use of oxy-fuel burners in industrial processes such as glass melting, permits the furnace designer to achieve varying flame momentum, glass melt coverage, and flame radiation characteristics. Examples of such burners and combustion processes are described in U.S. Pat. Nos. 5,256,058, 5,346,390, 5,547,368, and 5,575,637 the disclosures of which are incorporated herein by reference.
One particularly effective process and apparatus for utilizing oxy-fuel combustion in the manufacture of glass concerns staged combustion, which is disclosed in U.S. Pat. No. 5,611,682, the specification of which is incorporated herein by reference.
In the beginning of the 1990s, glass manufacturers began converting furnaces from air-fuel combustion to oxy-fuel combustion. Oxygen enrichment of some air-fuel systems has been accomplished where the oxygen concentration is increased up to about 30%. Higher oxygen concentrations in the range of 40-80% are not used because of the increased potential for forming NOx pollutants. It has also been found that using oxy-fuel combustion where oxygen is present in a concentration of between 90-100% results in more favorable economics for the user.
Many of the larger oxy-fuel glass furnaces are supplied by oxygen generated on site using well-known cryogenic or vacuum swing adsorption techniques. It is customary and, to date, the only method for backing up the supply of on-site generated oxygen is to keep an inventory of liquid oxygen at the same site. Thus, when the on-site generation facility is taken off-line either due to a process problem or for routine maintenance, the inventory of liquid oxygen is utilized to supply the oxygen for the oxy-fuel combustion. This method of backing up the on-site generated oxygen requires large insulated tanks for storage of the oxygen in liquid form and vaporizers to enable the liquid oxygen to be converted into gaseous oxygen for use in the oxy-fuel process. It is conventional to utilize trucks to haul liquid oxygen to the site from a larger air separation facility. Utilizing liquid oxygen back-up with an on-site generated oxygen system permits the user to continue using an oxy-fuel process without interruption. Any oxy-fuel combustion system, e.g. one of those disclosed in the above-referenced patents, would benefit from on-site production having a back-up system.
Until now, backing up oxy-fuel glass furnaces with an inventory of liquid oxygen has not been considered to be a problem. However, with the conversion of more and more furnaces at multi-furnace sites and the use of oxy-fuel combustion in flat or float glass furnaces which are much larger and use more oxygen, liquid oxygen backup becomes a significant concern to the user because of the high capital cost of storage tanks and vaporizers. In addition to the cost issue, a logistics problem arises relating to the transportation of the liquid oxygen to the site and having enough liquid oxygen available on short notice from a nearby air separation facility used to produce the liquid oxygen. Transportation of liquid oxygen to user sites in remote locations becomes even a greater problem fraught with greater difficulties.
Normally, when a glass furnace is converted from air-fuel to oxy-fuel, heat recovery devices such as regenerators and air supply systems are removed. For the user, one of the incentives to convert to oxy-fuel is reduced capital costs due to elimination of the heat recovery devices. Due to the design of oxy-fuel burners, the furnace cannot be operated by simply substituting air for oxygen in conventional combustion systems in use today. The pressure requirement to provide an equivalent amount of contained oxygen using air in an oxy-fuel burner would be extremely high, requiring an expensive air supply system. Further, some oxy-fuel burners would be sonic flow limited if fired at an equivalent firing rate.
When using oxy-fuel combustion where the oxygen supply is curtailed or disrupted, the conventional technique is to maintain the furnaces in a condition called xe2x80x9chot holdxe2x80x9d. Hot hold is a condition where production is stopped and the furnace is kept hot so that the glass does not solidify. Allowing the glass to solidify would severely damage the furnace. Several companies specialize in furnace heat-ups following cold furnace repairs. They use specially designed air-fuel burners to provide the initial increase in temperature in the furnace. In case of oxygen supply disruption, the same burners could be used to provide enough heating for hot hold. In this procedure, no special temperature profile for production would be attempted and the maximum temperature achieved by these devices could be about 2200xc2x0 F. This temperature is not sufficient for production of glass and is the least preferred option to be used by glass manufacturers. The cost of not producing glass is very high to the glass manufacturer, in terms of lost product sales as well as disruption of downstream glass forming lines.
Therefore, there is a definite need to provide a method and apparatus for maintaining production in a furnace used for glass manufacturing in the event of a curtailment or disruption in the availability of oxygen.
The present invention pertains to a method and apparatus to backup an oxy-fuel combustion system with an air-fuel combustion system that can be used with or oxygen enrichment to maintain production in an industrial furnace such as glass melting furnace. According to the present invention, a system has been devised which permits oxy-fuel, air-fuel, or an oxygen enriched air-fuel operation. The burner and burner block assembly according to the present invention permits the user to operate in different modes without replacing the burner block. Thus, the same burner block can be used for all modes of operation for providing combustion close to the glass for better heat transfer by introducing fuel underneath the oxidant in the air-fuel and oxygen enriched air-fuel operating modes. A burner according to the present invention can utilize oxygen enrichment to effect the process.
According to the present invention, a burner block, i.e. conventional burner block such as described in U.S. Pat. No. 5,611,682 can be used for either oxy-fuel or air-fuel combustion, allowing the combustion system to be rapidly converted between the two modes. According to the present invention, when a problem with oxygen supply occurs, the oxy-fuel burners would be turned off, disconnected, and replaced by air-fuel backup burners that have the same configuration for a connection to the burner block. With the air-fuel backup system, the user would retain the air supply systems from previous air-fuel systems used in the melting operation or, air blowers would be supplied as part of the back up system. Air-fuel burners according to the present invention should be capable of firing at rates substantially higher than the oxy-fuel burners.
In its"" broadest aspect the present invention pertains to using air or oxygen enriched air and fuel as a substitute for oxy-fuel combustion, in the event oxygen supply is diminished or interrupted in order to maintain heating in an industrial environment, the air or oxygen enriched air being introduced into the environment in sufficient volume with a fuel to effect the required level of heating. The substitution of air or oxygen enriched air-fuel combustion for oxy-fuel combustion can be made in any manner to achieve equivalent heating to that obtained using oxy-fuel combustion. In this aspect water cooling of the exhaust gases will be beneficial for lowering exhaust gas volume.
Thus, in one aspect the present invention is a process for maintaining heating of a furnace to an elevated temperature using oxy-fuel combustion, wherein an oxy-fuel flame is introduced into the furnace using an oxy-fuel burner, the burner having an oxy-fuel firing rate, and a separate oxidizer stream is introduced underneath the oxy-fuel flame, when oxygen supply for the flame and the oxidizer is eliminated or terminated comprising the steps of; introducing one of air or oxygen enriched air into said furnace in place of the oxy-fuel flame, and replacing the separate oxidizer stream with fuel and introducing the fuel into the furnace beneath the one of air or oxygen-enriched air to provide an air-fuel flame having a firing rate equal to or greater than the oxy-fuel firing rate to maintain the temperature in the furnace.
In another aspect, the present invention is a process for maintaining heating of a furnace to an elevated temperature using oxy-fuel combustion, wherein an oxy-fuel flame is introduced into the furnace using an oxy-fuel burner, the burner having an oxy-fuel firing rate, the burner mounted proximate a separate passage for introducing an auxiliary fluid, e.g. an oxidizer into the oxy-fuel flame, comprising the steps of; closing the separate passage during oxy-fuel combustion when oxygen supply for the flame is eliminated or terminated replacing the oxy-fuel flame with a stream of air or oxygen-enriched air, opening the separate passage and introducing a stream consisting of fuel into the furnace through the separate passage proximate the stream of air or oxygen-enriched air to provide an air-fuel flame having a firing rate equal to or greater than the oxy-fuel firing rate to maintain temperature in the furnace.
A further aspect of the present invention is a process for maintaining heating of a furnace, the furnace having a burner block having an upper passage and a lower passage the passages being co-extensive, to an elevated temperature using oxy-fuel combustion, wherein an oxy-fuel flame is introduced into the furnace using an oxy-fuel burner, the burner having an oxy-fuel firing rate, the oxy-fuel burner adapted to introduce the oxy-fuel flame through the upper passage of the burner block, comprising the steps of; closing the lower passage of the burner block when oxy-fuel combustion is used for heating the furnace, then when oxygen supply for the flame is eliminated or terminated, opening the lower passage of the burner block, introducing a stream consisting of air or oxygen-enriched air into the furnace through the upper passage, and introducing a stream consisting of fuel into the furnace through the lower passage to provide an air-fuel flame having a firing rate equal to or greater than the oxy-fuel firing rate to maintain the temperature in the furnace.
In yet a further aspect, the present invention is a combustion system of the type having an oxy-fuel burner adapted to produce an oxy-fuel flame with a burner block mounted on the burner, the burner having an oxy-fuel firing rate, the burner block having a first passage with a first end in fluid tight relation to a flame end of the burner and a second end adapted to direct the flame produced by the burner for heating in industrial environments and a second separate passage in the burner block disposed beneath and coextensive with the first passage, the second passage terminating in a nozzle end in the second end of the burner block to direct oxidizing fluid underneath and generally parallel to the oxy-fuel flame, the improvement comprising; first means to introduce one of air or oxygen enriched air through the burner into the burner block in place of the oxy-fuel flame, and second means to introduce fuel into the second separate passage in the burner block in place of the oxidizing fluid, thereby producing an air-fuel combustion flame with an air-fuel firing rate equal to or greater than the oxy-fuel firing rate, whereby the combustion system can continue to heat the industrial environment in the event supply of oxygen is interrupted or reduced.
A still further aspect, the present invention is a combustion system adapted to provide direct or staged combustion in a furnace using in oxy-fuel burner adapted to produce an oxy-fuel flame with a burner, the burner having an oxy-fuel firing rate, the burner used with a burner block having an upper passage and a lower passage the passages being co-extensive along separate but parallel axes, the burner mounted in fluid tight relationship to the burner block to permit the burner block to direct the oxy-fuel flame through the upper passage of the burner block with the lower passage of the burner block closed during non-staged oxy-fuel combustion thus permitting the combustion system to be changed from oxy-fuel combustion to air fuel combustion by introducing a stream consisting of air or oxygen enriched air through the burner into the furnace and opening the second passage and introducing a stream consisting of fuel into and through the second passage thereby enabling the combustion system to produce an air-fuel combustion flame with an air-fuel firing rate equal to or greater than the oxy-fuel firing rate, whereby the combustion system can continue to heat the industrial environment in the event the supply of oxygen is interrupted or reduced.
In still another aspect, the present invention is a combustion system of the type adapted to provide direct or staged combustion in a furnace using an oxy-fuel burner adapted to produce an oxy-fuel flame with a burner, the burner having an oxy-fuel firing rate, the burner used with a burner block having an upper passage and a lower passage, the passages being coextensive along separate but parallel axes, the burner mounted in fluid tight relationship to the burner block to permit the burner block to direct the oxy-fuel flame through the lower passage of the burner block with the upper passage of the burner block closed during oxy-fuel combustion, thus, permitting the combustion system to be changed from oxy-fuel combustion to air fuel combustion by introducing a fuel stream through the burner and into the furnace and opening the upper passage and introducing a stream consisting of air or oxygen enriched air into and through the upper passage, thereby enabling the combustion system to produce an air-fuel combustion flame with an air-fuel firing rate equal to or greater than the oxy-fuel firing rate, whereby the combustion system can continue to heat the furnace in the event the supply of oxygen is interrupted or reduced.
Thus another aspect, the present invention contemplates reducing exhaust gas volume in a furnace being heated according to the method and apparatus of the invention by liquid water cooling of the exhaust gases exiting the furnace. In this aspect the present invention is a process for maintaining heating of a furnace to an elevated temperature using oxy-fuel combustion, wherein an oxy-fuel flame is introduced into the furnace and exhaust gases exit the furnace, and wherein the exhaust gases must be cooled after exiting the furnace, when oxygen supplied for the oxy-fuel flame is eliminated or terminated, comprising the steps of: replacing the oxy-fuel flame with an air-fuel flame, the air fuel flame having a firing rate equal to or greater than the firing rate for the oxy-fuel flame, and cooling the exhaust gases exiting from the furnace through injection and evaporation of liquid water to decrease the volume of the exhaust gases.